Method and apparatus for invoking beamforming responsive to carrier transition

ABSTRACT

Disclosed herein is a method and corresponding apparatus to help manage wireless communication between a base station and a device served by the base. In accordance with the disclosure, when a base station transitions from serving the device on just a first carrier to serving the device on a combination of the first carrier and a second carrier, the base station will responsively take action to improve downlink communication to the device on the first carrier. In particular, the base station will respond to the occurrence of that transition by starting to beamform downlink transmission to the device on the first carrier.

REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. patent application Ser. No. 14/844,688,filed Sep. 3, 2015, the entirety of which is hereby incorporated byreference.

BACKGROUND

Unless otherwise indicated herein, the description provided in thissection is not itself prior art to the claims and is not admitted to beprior art by inclusion in this section.

A typical cellular wireless network includes a number of base stationseach radiating to provide coverage in which to serve user equipmentdevices (UEs) such as cell phones, tablet computers, tracking devices,embedded wireless modules, and other wirelessly equipped communicationdevices. In turn, each base station may be coupled with networkinfrastructure that provides connectivity with one or more transportnetworks, such as the public switched telephone network (PSTN) and/orthe Internet for instance. With this arrangement, a UE within coverageof the network may engage in air interface communication with a basestation and may thereby communicate via the base station with variousremote network entities or with other UEs served by the base station.

Further, a cellular wireless network may operate in accordance with aparticular air interface protocol or “radio access technology,” withcommunications from the base stations to UEs defining a downlink orforward link and communications from the UEs to the base stationsdefining an uplink or reverse link. Examples of existing air interfaceprotocols include, without limitation, Orthogonal Frequency DivisionMultiple Access (OFDMA (e.g., Long Term Evolution (LTE) and WirelessInteroperability for Microwave Access (WiMAX)), Code Division MultipleAccess (CDMA) (e.g., 1×RTT and 1×EV-DO), and Global System for MobileCommunications (GSM), among others. Each protocol may define its ownprocedures for registration of UEs, initiation of communications,handover between coverage areas, and other functions related to airinterface communication.

In practice, a base station may be configured to provide service onmultiple carrier frequencies or “carriers.” Each carrier could be a timedivision duplex (TDD) carrier that defines a single frequency channelmultiplexed over time between downlink and uplink use, or a frequencydivision duplex (FDD) carrier that defines two separate frequencychannels, one for downlink communication and one for uplinkcommunication. Each frequency channel of a carrier may then occupy aparticular frequency bandwidth defining a range of frequency at aparticular position (e.g., defined by a center frequency) in the radiofrequency spectrum. As such, carriers may differ in width from eachother and reside at different frequencies than each other. For instance,industry standards define certain TDD carriers to be 20 MHz wide and toreside in the relatively high 2.5 GHz frequency band, and certain FDDcarriers to be 5 or 10 MHz wide (per channel) and to reside in therelatively low 800 MHz frequency band. Other examples exist as well.

Each carrier may also define various logical channels to facilitatecommunication between the base station and one or more served UEs. Forinstance, on the downlink, a carrier may define a reference channel onwhich the base station broadcasts a reference signal useable by UEs todetect and evaluate coverage, various other downlink control channels tocarry control signaling (such as resource-scheduling directives) to UEs,and one or more shared or traffic channels for carrying bearer data(e.g., user or application level data) to UEs. And on the uplink, acarrier may define one or more uplink control channels to carry controlsignaling (such as resource scheduling requests, channel state reports,and the like) from UEs, and one or more shared or traffic channels forcarrying bearer data from UEs.

When a UE enters into coverage of a base station on a particularcarrier, the UE may attach or register with the base station on thatcarrier, and the base station may then serve the UE on that carrier.Further, under certain air interface protocols, a base station may beable to serve a UE concurrently on multiple carriers, to help increasethe effective bandwidth and associated throughput available to the UE.For instance, if a UE is attached with a base station on a firstcarrier, the base station may then add a second carrier to its serviceof the UE so as to then provide the UE with “carrier aggregation”service on a combination of the first carrier and the second carrier. Inthat arrangement, the first carrier may be considered the UE's primarycarrier or primary cell (PCell), and the second carrier may beconsidered the UE's secondary carrier or secondary cell (SCell).Depending on the carrier aggregation implementation, the SCell might beused principally for downlink communication (to increase the UE'sdownlink throughput) rather than for uplink communication, and the PCellmay carry some or all control signaling related to the SCell (inaddition to control signaling related to the PCell).

Overview

When a base station provides service on multiple carriers, thedifference in frequency between the carriers may result in the basestation providing a different range of coverage per carrier. This stemsfrom the fact that lower frequency signals have less path loss and thustend to propagate farther from the base station than higher frequencysignals at the same transmission power. Thus, if a base station providesservice on a first carrier at a high frequency and on a second carrierat a low frequency, the base station's coverage on the first carrierwill likely extend a shorter distance from the base station than thebase station's coverage on the second carrier.

A specific example of this may occur with the above noted TDD and FDDcarriers, due to the TDD carriers residing in the relatively high 2.5GHz frequency band and thus having relatively high path loss, and theFDD carriers residing in the relatively low 800 MHz frequency band andthus having relatively low path loss. If a base station is configured toprovide service on both such a TDD carrier and such an FDD carrier, thebase station's range of coverage on the TDD carrier would thus extend ashorter distance from the base station than the base station's range ofcoverage on the FDD carrier, for a given level of transmission power.

Further, when a base station serves a UE on a given carrier, the basestation's maximum downlink transmission power to the UE is typicallyhigher than the UE's maximum uplink transmission power to the basestation. Consequently, on the same or similar frequency (and thus withthe same or similar path loss), the effective uplink coverage areabetween the base station the UE will typically be smaller than theeffective downlink coverage area between the base station and the UE.

As a result of these differences in carrier frequency and in uplink anddownlink transmission power, when a base station provides coverage ontwo carriers, the base station may effectively have four separatecoverage borders defining areas in which the base station can engage incommunication with served UEs. In particular, the base station may haveseparate coverage borders corresponding respectively with (i) relativelylow power uplink on the higher frequency carrier, (ii) relatively highpower downlink on the higher frequency carrier, (iii) relatively lowpower uplink on the lower frequency carrier, and (iv) relatively highpower downlink on the lower frequency carrier.

FIG. 1 depicts this by way of example, in an arrangement where a basestation 12 provides service on a first carrier that is at a relativelyhigh frequency (e.g., a TDD carrier) and a second carrier that is at arelative low frequency (e.g., an FDD carrier). As shown in FIG. 1, thebase station in this example effectively provides coverage extending outto (i) a first border 14 on the uplink of the first carrier, (ii) asecond border 16 on the downlink of the first carrier, (iii) a thirdborder 18 on the uplink of the second carrier, and (iv) a fourth border20 on the downlink of the second carrier. Of course, other arrangementsare possible as well. For instance, in another arrangement, the downlinkof the first carrier may extend farther from the base station than theuplink of the second carrier. Moreover these effective coverage borderscould change over time due to variations in load, interference, andother issues.

With an arrangement like this, one problem that can arise is that a UEserved by the base station on just one of the base station's carriersmay transition to a situation where the UE still has downlink coverageon that carrier but no longer has sufficient uplink coverage on thatcarrier. For instance, in the arrangement of FIG. 1, a UE may be servedby the base station on just the first carrier while the UE is atposition A, where the UE and base station can engage uplink and downlinkbearer communication on the first carrier, but the UE may then movefarther away from the base station and reach position B. When the UEreaches position B, the UE may then no longer be able to engage inuplink bearer communication to the base station on the first carrier,but the UE may still be able to receive downlink bearer communicationfrom the base station on the first carrier. In practice, the basestation may learn of this situation by detecting threshold low uplinksignal strength from the UE on the first carrier, or by receiving areport that the UE is receiving low enough downlink signal strength onthe first carrier to suggest that the UE's uplink signal strength on thefirst carrier would be insufficient.

In this situation, to enable the UE to continue engaging in both uplinkand downlink bearer communication with the base station, the basestation may invoke carrier aggregation for the UE, by adding the secondcarrier to the UE's service. For instance, the base station may engagein control signaling with the UE to inform the UE that the first carrierwill be the UE's PCell and that the second carrier is added as an SCellfor the UE. Alternatively, given the insufficiency of the UE's uplinkcoverage on the first carrier and given that a PCell in carrieraggregation may need to carry uplink signaling related to both the PCelland each added SCell, the base station may transition (e.g., redirect orhand over) the UE from the first carrier to the second carrier and theninform the UE that the second carrier will be the UE's PCell and thatthe first carrier is added as an SCell.

Through this or another process, a base station may thus transition fromserving a UE on just a first carrier to serving the UE on a combinationof the first carrier and a second carrier. Further, the occurrence ofsuch a transition may indicate or be associated with the fact that theUE was at or near an edge of the base station's coverage on the firstcarrier and that the UE's downlink coverage on that first carrier maynot be particularly optimal—e.g., that the UE may not have optimaldownlink throughput on the first carrier. In addition, the fact that thebase station has transitioned to serve the UE with carrier aggregationservice on a combination of the first carrier and the second carrier maynot entirely overcome that problem. For instance, it is possible thatthe first carrier may be relatively wide (e.g., a 20 MHz wide TDDcarrier) and thus support relatively high peak throughput, whereas theadded second carrier may be relatively narrow (e.g., a 5 or 10 MHz wideFDD carrier) and may thus support lower peak throughput. Thus, the basestation's addition of the second carrier to the UE's service may notsufficiently improve the UE's downlink service.

Disclosed herein is a method and corresponding apparatus to help addresssuch an issue. In accordance with the disclosure, when a base stationtransitions from serving a UE on just a first carrier to serving the UEon a combination of the first carrier and a second carrier, the basestation will responsively take action to improve downlink communicationto the UE on the first carrier. In particular, the base station willrespond to the occurrence of that transition by starting to beamformdownlink transmission to the UE on the first carrier.

When a base station operates on a particular carrier, the base station'santenna structure may normally provide a radiation pattern thatgenerally defines a scope of coverage in which the base station canengage in downlink communication to UEs. To facilitate the presentmethod, however, the base station may also be configured to selectivelybeamform (i.e., focus) downlink transmission on that carrier toparticular UEs. To beamform transmission to a UE, for instance, the basestation may receive from the UE certain uplink control signaling thatcarries or embodies particular information regarding the path oftransmission from the UE (such as phase information, precoding matrixinformation, or the like), and the base station may use that informationin as a basis to dynamically direct downlink transmission in the reversedirection, i.e., with a beam directed to the UE's location. Otherbeamforming mechanisms may be also possible.

Thus, in accordance with the present disclosure, the base station mayinitially serve the UE on just a first carrier without beamforming(i.e., just using the base station's general downlink radiation patternon the first carrier and not beamforming downlink transmission to theUE) and may then transition from serving the UE on the first carrier toserving the UE on a combination of the first carrier and a secondcarrier. And in response to that transition, the base station may theninvoke downlink beamforming to the UE on the first carrier, so as tohelp improve downlink communication to the UE on the first carrier andperhaps to improve or provide a more consistent user experience.

Accordingly, in one respect, disclosed is method for controllingwireless communication between a base station and a UE served by thebase station. According to the method, the base station serves the UE onjust a first carrier, the base station then transitions from serving theUE on just the first carrier to serving the UE on a combination of thefirst carrier and a second carrier, and, responsive to at least thattransitioning, the base station starts to apply beamforming to the UE onthe first carrier.

Further, in another respect, the disclosed method may involve the basestation serving the UE on just a TDD carrier in a first frequency band,including providing downlink transmission to the UE on the TDD carrierand not beamforming the downlink transmission. In turn, the method mayinvolve the base station transitioning from serving the UE on just theTDD carrier in the first frequency band to providing the UE with carrieraggregation service on a combination of the TDD carrier in the firstfrequency band and an FDD carrier in a second frequency band, with theFDD carrier being a primary component carrier of the carrier aggregationservice and the TDD carrier being a secondary component carrier of thecarrier aggregation service, and the second frequency band being lowerin frequency than the first frequency band. Further, the method may theninvolve, responsive to at least the transitioning from serving the UE onjust the TDD carrier in the first frequency band to providing the UEwith carrier aggregation service on a combination of the TDD carrier inthe first frequency band and the FDD carrier in the second, lowerfrequency band, the base station starting to beamform downlinktransmission to the UE on the TDD carrier.

And still further, in another respect, disclosed is a base stationconfigured to control wireless communication between the base stationand a UE served by the base station in the above or similar ways. Asdisclosed, for instance, the base station may comprise a wirelesscommunication interface having an antenna structure, that is operable toprovide downlink transmission to the UE and to receive uplinktransmission from the UE. And the base station may comprise a controllerthat is operable to control the downlink transmission from the basestation the UE on a first carrier. In line with the discussion above,the controller may thus cause the base station to carry out operationscomprising (i) serving the UE on just the first carrier and withoutbeamforming of downlink transmission from the base station to the UE onthe first carrier, (ii) transitioning from serving the UE on just thefirst carrier to serving the UE on a combination of the first carrierand a second carrier and (iii) responsive to at least the transitioning,starting to beamform downlink transmission to the UE on the firstcarrier.

These as well as other aspects, advantages, and alternatives will becomeapparent to those of ordinary skill in the art by reading the followingdetailed description, with reference where appropriate to theaccompanying drawings. Further, it should be understood that thedescriptions provided in this overview and below are intended toillustrate the invention by way of example only and not by way oflimitation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of example coverage borders provided foruplink and downlink service on multiple carriers.

FIG. 2 is a simplified block diagram of an example wirelesscommunication system in which embodiments of the present disclosure canbe implemented.

FIG. 3 is a simplified block diagram of an example base station operableto implement embodiments of the present disclosure.

FIG. 4 is a flow chart depicting an example method in accordance withthe present disclosure.

FIG. 5 is a flow chart depicting another example method in accordancewith the present disclosure.

DETAILED DESCRIPTION

The present method and system will be described herein in the context ofLTE, and with the first carrier being a TDD carrier in the 2.5 GHz bandand the second carrier being an FDD carrier in the 800 MHz band.However, it will be understood that principles of the disclosure canextend to apply in other scenarios as well, such as with respect toother air interface protocols and other carriers. Further, even withinthe context of LTE and with the example carriers, numerous variationsfrom the details disclosed herein may be possible. For instance,elements, arrangements, and functions may be added, removed, combined,distributed, or otherwise modified. In addition, it will be understoodthat functions described here as being performed by one or more entitiesmay be implemented in various ways, such as by a processor executingsoftware instructions for instance.

Referring to the drawings, as noted above, FIG. 2 is a simplified blockdiagram of an example wireless communication system in which the presentmethod can be implemented. In particular, FIG. 2 depicts arepresentative LTE network, which functions primarily to serve UEs withwireless packet data communication service, including possibly voiceover Internet Protocol (VoIP) service, but may also provide otherfunctions. As shown, the LTE network includes a representative LTE basestation 22 known as an evolved Node B (eNodeB). The eNodeB has anantenna structure (e.g., patch, dipole, phased array, and/or otherantenna arrangement) and associated equipment for providing LTE coveragein which to serve UEs such as an example UE 24.

In line with the discussion above, the eNodeB may be configured with oneor more radios to provide service on multiple carriers, each of whichmight be in the same or a different band in the radio frequencyspectrum, and the eNodeB may operate with higher transmission power thanthe UE, so that there may be multiple effective coverage borders atvarying distances from the eNodeB. By way of example, as noted above,the eNodeB may be configured to provide service on a TDD carrier in the2.5 GHz band and an FDD carrier in the 800 MHz band.

In the example system eNodeB 22 has a communication interface with amobility management entity (MME) 26, which may function as a signalingcontroller for the LTE network. Further, eNodeB 22 has a communicationinterface with a serving gateway (SGW) 28, which in turn has acommunication interface with a packet-data network gateway (PGW) 30 thatprovides connectivity with a packet-switched network 32, and the MME 26has a communication interface with the SGW 28. In practice, each ofthese entities may sit on a core packet network operated by a wirelessservice provider, and the communication interfaces between theseentities may be logical packet-switched interfaces. Other arrangementsare possible as well.

FIG. 3 is next a simplified block diagram of a representative basestation such as eNodeB 22, depicting some of the components that can beincluded in such an entity. Generally, this base station could takevarious forms, such as a macro base station having a tall antenna towerand power amplifier to provide a wide range of coverage, or a small basestation (such as a picocell, femtocell, small cell, mini macro basestation, relay base station, mobile hotspot, or the like), having asmaller form factor and lower power and thus providing a relativelysmaller range of coverage. As shown in FIG. 3, the representative basestation may include, among other elements, a wireless communicationinterface 34 and a controller 36, which may be integrated together orcommunicatively linked together by a system bus, network, or otherconnection mechanism 38.

As shown, wireless communication interface 34 may include an antennaarrangement 40, which may be tower mounted or provided in another form,and associated components such as a power amplifier 42 and one or moreradio units 44 for engaging in air interface communication with UEs viathe antenna arrangement 40, so as to transmit bearer data and controlsignaling to the UEs and to receive bearer data and control signalingfrom the UEs. In the example arrangement, the radio unit(s) would beconfigured to engage in communication via the antenna arrangement oneach of multiple carriers, such as the representative TDD and FDDcarriers and perhaps others. In general, the eNodeB may thus generallyprovide a radiation pattern respectively on each carrier, with theeNodeB's FDD coverage likely extending farther from the base stationthan the TDD coverage as discussed above, because the FDD carrier is ina substantially lower frequency band (with less path loss) than the TDDcarrier.

Controller 36 may then include a processing unit 46 (e.g., one or moregeneral purpose and/or special purpose processors) and non-transitorydata storage 48 (e.g., one or more volatile and/or non-volatile storagecomponents such as magnetic, optical, flash or other storage, possiblyintegrated in whole or in part with the processing unit). And datastorage 48 may hold (e.g., have encoded thereon) program instructions50, which may be executable by processing unit 46 to carry out or causeto be carried out various base station operations described herein.Although the controller 36 is shown within the base station, some or allof the control functionality could alternatively be provided external tothe base station, such as by another entity in the network.

In practice, when UE 24 enters into coverage of eNodeB 22, the UE maydetect coverage of the eNodeB 22 on a particular carrier, such as theeNodeB's TDD carrier, and the UE and eNodeB may then engage in controlsignaling to establish a radio resource configuration (RRC) connectionon that carrier between the UE and the eNodeB. Further, the UE and theeNodeB may engage in an attach process through which the networkestablishes for the UE a bearer connection between the UE and the PGWvia the eNodeB and SGW, and through which the eNodeB establishes for theUE a context record indicating that the eNodeB is serving the UE on thecarrier. In particular, the context record may indicate that the UE'sRRC connection encompasses just that one carrier, designating thecarrier by a global carrier index number for instance. Further, the UEmay also establish a context record indicating the carrier on which theUE is being served by the eNodeB.

When the UE is so attached with the eNodeB and served on the carrier,the UE may regularly measure downlink signal strength from the eNodeB onthe carrier and may transmit channel state report signaling to theeNodeB so as to inform the eNodeB of the UE's channel conditions.Further, the UE may regularly transmit an uplink reference signal thatthe eNodeB may monitor to help further appreciate the UE's channelconditions.

When the eNodeB has bearer data to transmit to the UE on the UE's servedcarrier, the eNodeB may transmit on a downlink control channel to the UEa downlink control information (DCI) message indicating certain radioresources (e.g., physical resource blocks) of a downlink shared channelon which the eNodeB is transmitting the data to the UE, and the eNodeBmay transmit the data in the indicated radio resources using amodulation and coding scheme (and thus data rate) suitable for the UE'scurrent channel conditions, for receipt by the UE. Similarly, when theUE has bearer data to transmit to the eNodeB, the UE may transmit ascheduling request or the like on an uplink control channel to theeNodeB, and the eNodeB may then transmit to the UE a DCI messageindicating certain radio resources of an uplink shared channel on whichthe UE should transmit the data to the eNodeB, and the UE may thentransmit the data in the indicated radio resources using a suitablemodulation and coding scheme, for receipt by the eNodeB.

When the eNodeB is serving the UE on just the first carrier, the eNodeBmay be doing so without downlink beamforming to the UE. Thus, downlinktransmissions from the eNodeB to the UE may be provided generally inaccordance with the eNodeB's downlink radiation pattern rather thanbeing focused specifically in the direction of the UE.

In a situation such as that depicted in FIG. 1 and discussed above, whenthe eNodeB is serving the UE on just a single carrier like this, theeNodeB may then transition to begin serving the UE with carrieraggregation on a combination of the first carrier and a second carrier,such as the eNodeB's FDD carrier for instance. To do so, as discussedabove, the eNodeB may transition the UE from the first carrier to thesecond carrier and may designate the second carrier as the UE's PCelland the first carrier as an SCell for the UE. For instance, the eNodeBmay transmit RRC reconfiguration signaling to the UE to redirect or handover the UE to the second carrier and to designate the second carrier bya carrier index number that the UE interprets to mean the second carrieris a PCell and to designate the first carrier by a carrier index numberthat the UE interprets to mean that the first carrier is an SCell. TheeNodeB may then provide the UE with carrier aggregation service on thesetwo carriers (possibly including one or more others as well). Further,the eNodeB may update its context record for the UE to indicate thecarriers on which the eNodeB is now serving the UE, and the UE maysimilarly update its records.

With such carrier aggregation service, the UE may regularly monitorsignal strength of each carrier and transmit channel state reports forboth carriers on a control channel of the PCell or alternatively on anuplink of each respective carrier. Further, the eNodeB may scheduleconcurrent bearer communication with the UE on both carriers to helpprovide the UE with improved throughput, transmitting DCI messaging tothe UE on a downlink control channel of the PCell or alternatively ondownlink control channels of each respective carrier. The eNodeB may,however, limit such scheduled communications in view of coverageavailable. For instance, given that the UE's uplink coverage on thefirst carrier is threshold poor, the eNodeB may avoid scheduling uplinkbearer communication with the UE on the first carrier. But the eNodeBmay schedule uplink bearer communication with the UE on the secondcarrier, and the eNodeB may schedule uplink and downlink bearercommunication with the UE on the second carrier.

As discussed above, per the present disclosure, the eNodeB may invokebeamforming on the first carrier in response to the eNodeB transitioningfrom serving the UE on just a first carrier to serving the UE on acombination of the first carrier and a second carrier. This responsiveaction could occur during or after the transition occurs, or perhapseven before the transition occurs but in response to determining thatthe transition is going to occur (which could be considered stillresponding to the transition).

In line with the discussion above, to begin beamforming to the UE on thefirst carrier, the eNodeB may use uplink control signaling as a basis todirect transmission on the first carrier to the UE. By way of example,the UE could transmit an uplink reference signal on the first carrier(which may reach the eNodeB, even though the first carrier uplink mightbe insufficient to successfully carrier bearer data to the eNodeB), andthe eNodeB may use phase information or the like from that signal as abasis to set phases and other attributes of downlink transmission to theUE on the first carrier so as to focus an antenna path in the directionof the UE. Alternatively, the UE could transmit precoding matrixinformation or the like in a control signal on the first carrier or thesecond carrier, which the eNodeB could use as a basis to beamform to theUE on the first carrier. Still alternatively, the eNodeB could use anuplink reference signal from the UE on the second carrier as a basis todetermine a direction for focused transmission to the UE, and the eNodeBcould apply that determination on the first carrier. And yetalternatively, the eNodeB might be able to use geo-location of the UE asa basis to direct transmission to the UE on the first carrier.Advantageously, this beamforming may thus improve downlink service tothe UE on the first carrier.

Note that in an example arrangement such as that depicted in FIG. 1, theeNodeB may limit this process to UEs that are just within the areabetween the first border 14 and the second border 16, i.e. where thefirst carrier provides sufficient downlink but insufficient uplink andwhere the second carrier provides sufficient uplink and downlink.Alternatively or additionally, the eNodeB could so limit this processonly if the eNodeB is currently beamforming to more than a predefinedthreshold number of UEs on the first carrier (given processinglimitations at the eNodeB).

FIG. 4 is next a flow chart depicting example operations of a methodthat could be carried out by a base station in accordance with thepresent disclosure, to control wireless communications between the basestation a UE served by the base station. As shown in FIG. 4, at block52, the method involves the base station serving the UE on just a firstcarrier. In turn, at block 54, the method involves the base stationtransitioning from serving the UE on just the first carrier to servingthe UE on a combination of the first carrier and a second carrier. Andat block 56, the method involves, responsive to at least thetransitioning, the base station starting to apply beamforming to the UEon the first carrier.

In this method, the first and second carriers can take various forms,and details of the transitioning and beamforming may vary as well.

By way of example, the first carrier could be a TDD carrier, the secondcarrier could be an FDD carrier, and the act of serving the UE on thecombination of the TDD carrier and the FDD carrier may involve providingthe UE with carrier aggregation service with the FDD carrier being aprimary component carrier and the TDD carrier being a secondarycomponent carrier. Further, the act of starting to apply beamforming tothe UE on the first carrier could be additionally responsive to the factthat the transitioning is from serving the UE on jus the TDD carrier toserving the UE on a combination of the TDD carrier and the FDD carrier(i.e., not just to the fact of the transition but also to the fact thatthose are the carriers involved in the transition).

As another example, or phrased in another way, the first carrier couldoccupy a first frequency bandwidth, the second carrier could occupy asecond frequency bandwidth that is lower in frequency than the firstfrequency bandwidth, and the act of starting to apply beamforming couldbe additionally responsive to the second frequency bandwidth of thesecond carrier is lower in frequency than the first frequency bandwidthof the first carrier. And alternatively or additionally, the firstcarrier could occupy a first frequency bandwidth, the second carriercould occupy a second frequency bandwidth that is narrower in frequencythan the first frequency bandwidth, and the act of starting to applybeamforming could be additionally responsive to the second frequencybandwidth of the second carrier being narrower in frequency than thefirst frequency bandwidth of the first carrier.

Further, in these or other arrangements, the act of transitioning the UEfrom being served on just the first carrier to being served on acombination of the first carrier and the second carrier could involve(i) handing over the UE from service on the first carrier to service onthe second carrier and (ii) adding the first carrier to service of theUE as a secondary carrier, with the base station then engaging indownlink bearer communication with the UE on both the first carrier andthe second carrier and engaging in uplink bearer communication with theUE on just the second carrier (i.e., using the first carrier as asecondary carrier for carrying bearer data from the base station to theUE).

Further in line with the discussion above, before the transitioningoccurs, the base station may not be applying beamforming of downlinktransmission to the UE on the first carrier, and the act of starting toapply beamforming to the UE on the first carrier may involve the basestation starting to beamform downlink transmission to the UE on thefirst carrier. For instance, the base station may start to use uplinksignaling from the UE as a basis to beamform downlink transmission tothe UE on the first carrier. Moreover, before the transitioning occurs,the base station may be serving the UE with uplink bearer communicationon the first carrier and downlink bearer communication on the firstcarrier, and the transitioning may then involve the base stationdiscontinuing serving of the UE with uplink bearer communication on thefirst carrier and instead serving the UE with uplink bearercommunication on the second carrier, and perhaps serving the UE withdownlink bearer communication on both.

FIG. 5 is next another flow chart depicting example operations of amethod that could be carried out by a base station in accordance withthe present disclosure, to control wireless communications between thebase station a UE served by the base station. As shown in FIG. 6, atblock 58, the method involves the base station serving the UE on just aTDD carrier in a first frequency band, wherein the base station providesdownlink transmission to the UE on the TDD carrier and does not beamformthe downlink transmission. In turn, at block 60, the method involves thebase station transitioning from serving the UE on just the TDD carrierin the first frequency band to providing the UE with carrier aggregationservice on a combination of the TDD carrier in the first frequency bandand an FDD carrier in a second frequency band, with the FDD carrierbeing a primary component carrier of the carrier aggregation service andthe TDD carrier being a secondary component carrier of the carrieraggregation service, and with the second frequency band being lower infrequency than the first frequency band. And at block 62, the methodinvolves, responsive to at least the transitioning from serving the UEon just the TDD carrier in the first frequency band to providing the UEwith carrier aggregation service on a combination of the TDD carrier inthe first frequency band and the FDD carrier in the second, lowerfrequency band, the base station starting to beamform downlinktransmission to the UE on at least the TDD carrier, such as beginning touse uplink signaling from the UE as a basis to direct the downlinkbearer communication to a location of the UE.

Exemplary embodiments have been described above. Those skilled in theart will understand, however, that changes and modifications may be madeto these embodiments without departing from the true scope and spirit ofthe invention.

We claim:
 1. A method for controlling wireless communication between abase station and a user equipment device (UE) served by the basestation, the method comprising: the base station serving the UE on justa first carrier; the base station transitioning from serving the UE onjust the first carrier to serving the UE on a combination of the firstcarrier and a second carrier, wherein transitioning to serve the UE onthe combination of the first carrier and the second carrier compriseshanding over the UE from service on the first carrier to service on thesecond carrier and designating the second carrier as a primary carrierof the UE and the first carrier as a secondary carrier of the UE,wherein the base station then schedules concurrent bearer communicationwith the UE on the first carrier and the second carrier; and responsiveto at least the transitioning, the base station starting to applybeamforming to the UE on the first carrier, wherein starting to applybeamforming to the UE on the first carrier comprises starting to useuplink signaling from the UE as a basis to beamform downlinktransmission to the UE on the first carrier.
 2. The method of claim 1,wherein the first carrier occupies a first frequency bandwidth, whereinthe second carrier occupies a second frequency bandwidth that is lowerin frequency than the first frequency bandwidth, and wherein starting toapply beamforming is further responsive to the second frequencybandwidth of the second carrier being lower in frequency than the firstfrequency bandwidth of the first carrier.
 3. The method of claim 1,wherein the first carrier occupies a first frequency bandwidth, whereinthe second carrier occupies a second frequency bandwidth that isnarrower in frequency than the first frequency bandwidth, and whereinstarting to apply beamforming is further responsive to the secondfrequency bandwidth of the second carrier being narrower in frequencythan the first frequency bandwidth of the first carrier.
 4. The methodof claim 1, wherein before the transitioning, the base station does notbeamform downlink transmission to the UE on the first carrier, andwherein starting to apply beamforming to the UE on the first carriercomprises starting to beamform downlink transmission to the UE on thefirst carrier.
 5. The method of claim 1, wherein before thetransitioning, the base station serves the UE with uplink bearercommunication on the first carrier and downlink bearer communication onthe first carrier, and wherein the transitioning comprises discontinuingserving of the UE with uplink bearer communication on the first carrierand instead serving the UE with uplink bearer communication on thesecond carrier.
 6. A base station configured to control wirelesscommunication between the base station and a user equipment device (UE)served by the base station, the base station comprising: a wirelesscommunication interface including an antenna structure, operable toprovide downlink transmission to the UE and to receive uplinktransmission from the UE; and a controller operable to control thedownlink transmission from the base station the UE on a first carrier,wherein the controller is operable to cause the base station to carryout operations comprising (i) serving the UE on just the first carrierand without beamforming of downlink transmission from the base stationto the UE on the first carrier, (ii) transitioning from serving the UEon just the first carrier to serving the UE on a combination of thefirst carrier and a second carrier and (iii) responsive to at least thetransitioning, starting to beamform downlink transmission to the UE onthe first carrier, wherein starting to beamform downlink transmission tothe UE on the first carrier comprises starting to use uplink signalingfrom the UE as a basis to beamform the downlink transmission to the UEon the first carrier, wherein transitioning from serving the UE on justthe first carrier to serving the UE on the combination of the firstcarrier and the second carrier comprises handing over the UE fromservice on the first carrier to service on the second carrier anddesignating the second carrier as a primary carrier of the UE and thefirst carrier as a secondary carrier of the UE, wherein the base stationthen schedules concurrent bearer communication with the UE on the firstcarrier and the second carrier.
 7. The base station of claim 6, whereinthe controller comprises a processing unit, non-transitory data storage,and program instructions stored in the data storage and executable bythe processing unit to cause the base station to carry out theoperations.
 8. The base station of claim 6, wherein the first carrieroccupies a first frequency bandwidth, wherein the second carrieroccupies a second frequency bandwidth that is lower in frequency thanthe first frequency bandwidth, and wherein starting to beamform downlinktransmission to the UE on the first carrier is further responsive to thesecond frequency bandwidth of the second carrier being lower infrequency than the first frequency bandwidth of the first carrier. 9.The base station of claim 6, wherein the first carrier occupies a firstfrequency bandwidth, wherein the second carrier occupies a secondfrequency bandwidth that is narrower in frequency than the firstfrequency bandwidth, and wherein starting to beamform downlinktransmission to the UE on the first carrier is further responsive to thesecond frequency bandwidth of the second carrier being narrower infrequency than the first frequency bandwidth of the first carrier. 10.The base station of claim 6, wherein before the transitioning, the basestation serves the UE with uplink bearer communication on the firstcarrier and downlink bearer communication on the first carrier, andwherein the transitioning comprises discontinuing serving of the UE withuplink bearer communication on the first carrier and instead serving theUE with uplink bearer communication on the second carrier.
 11. A methodcomprising: transitioning by a base station from serving a userequipment device (UE) on just a first carrier to serving the UE on acombination of the first carrier and a second carrier, wherein thetransitioning includes designating the second carrier as a primarycarrier for carrier-aggregation service of the UE and the first carrieras a secondary carrier for the carrier-aggregation service of the UE,whereby the base station then schedules concurrent bearer communicationwith the UE on the first carrier and the second carrier; and responsiveto at least the transitioning, starting to beamform downlinktransmission to the UE on the first carrier, wherein starting to applybeamforming to the UE on the first carrier comprises starting to useuplink signaling from the UE as a basis to beamform downlinktransmission to the UE on the first carrier.
 12. The method of claim 11,wherein the first carrier occupies a first frequency bandwidth, whereinthe second carrier occupies a second frequency bandwidth that is lowerin frequency than the first frequency bandwidth, and wherein starting tobeamform downlink transmission to the UE on the first carrier is furtherresponsive to the second frequency bandwidth of the second carrier beinglower in frequency than the first frequency bandwidth of the firstcarrier.
 13. The method of claim 11, wherein the first carrier occupiesa first frequency bandwidth, wherein the second carrier occupies asecond frequency bandwidth that is narrower in frequency than the firstfrequency bandwidth, and wherein starting to beamform downlinktransmission to the UE on the first carrier is further responsive to thesecond frequency bandwidth of the second carrier being narrower infrequency than the first frequency bandwidth of the first carrier. 14.The method of claim 11, wherein before the transitioning, the basestation does not beamform downlink transmission to the UE on the firstcarrier.
 15. The method of claim 11, wherein before the transitioning,the base station serves the UE with uplink bearer communication on thefirst carrier and downlink bearer communication on the first carrier,and wherein the transitioning comprises discontinuing serving of the UEwith uplink bearer communication on the first carrier and insteadserving the UE with uplink bearer communication on the second carrier.